This invention relates to a fiber reinforced plastic rod, an apparatus, and methods for making and postforming the rod.
Thermoplastic and thermoset rods have been reinforced with continuous longitudinally aligned unidirectional fibers of glass, carbon, aramid, steel or hybrid fibers for uses in torsion and coil springs and other manufactured products requiring bent shapes.
When continuous fiber reinforced rods are used for applications which require bending of the rods, longitudinally aligned fibers in the rods buckle in the inside radius of the bend, the arc length of which is comparatively shorter than the longer arc length for the same length fibers on the outside radius of the bend. This buckling of the reinforcing fibers causes distortions in the intended shape, delamination, significant uncontrolled loss of mechanical strength, and difficulty in postforming the coil, torsion spring or other part.
Reinforced plastic rods with longitudinally aligned fibers are not particularly suited to resisting torque and resist shaping during manufacture into coil springs, torsion springs, or other shapes requiring bends. This problem has been addressed by forming coil springs by winding a braided fiber reinforced composite around a mandrel while the polymer matrix is fluid and allowing the resulting article to cure or solidify.